Bicycle helmets with aerodynamic outer shells have been used in disciplines in which reduced drag is an important consideration. For instance, in cycling disciplines such as track, triathlons and time trials, it is desired to reduce the drag caused by the racer. As the rider's head is located at a front of the bicycle when the rider is in a racing stance, headwear may be an important source of drag. Accordingly, bicycle helmets with aerodynamic outer surfaces have been created for such disciplines. In comparison with other bicycle helmets which have a plurality of vent holes, aerodynamic bicycle helmets have fewer ventilation holes in favour of a smoother continuous surface having increased streamline properties. Such aerodynamic bicycle helmets typically cover the ears of the rider, as the ears may be a source of drag.
Among the various factors in designing such helmets, the volume of the helmet may be kept as small as possible, without having an impact on the safety features of the helmet. Moreover, the outer shell of such helmets may often come as close as possible to the head of the wearer, especially at the bottom edge of the outer shell, to conform to the rider's anatomy. As the bottom edge of the outer shell of such helmets is often below the ears to cover same, it may be a challenge to install such a helmet on one's head. Such aerodynamic helmets have been conventionally plastically deformable at the bottom edge to fit one's head through the opening. However, this may result in a gradual deformation of the helmet and hence impact the aerodynamic properties thereof and/or result in painful pressure on the wearer's head.